The biosynthesis of retinal cell membranes is being explored using new techniques of immunochemical subcellular fractionation. The approach uses recently prepared antibodies against two proteins of the rod outer segment. Antibody to frog opsin prepared in rabbits and to cattle opsin prepared in sheep are being used as probes to study the vectorial transport of newly synthesized opsin from the Golgi apparatus to the rod outer segment. Membranes are labeled using radioactive amino acid precursors injected into the vitreous cavity of the frog eye. Subfractionation of the retina yields fragments intensely labeled at transient periods after the injection of radioactive amino-acids. The label appears predominantly in two proteins, opsin, and a large molecular weight protein of molecular weight 290,000. We have shown, by immunocytochemical techniques, that this protein is localized to the incisures of the rod outer segment. Accordingly this large protein has now been named incisin. Antibodies are to be linked to solid supports such as Sepharose beads or to polyethylene oxide to be used as an affinity purification of the newly synthesized opsin. Binding of the labeled newly synthesized opsin to the antibodies will be tested. Synthesis of the N-terminal portion of rhodopsin will provide a useful immunochemical probe for the orientation of rhodopsin in the disc and its orientation during transport to the disc. Synthesis of this peptide by the solid phase Merrifield technique will provide the antigenic determinant for immunization and for site-specific immunoabsorbent preparation. Since this peptide underlies two of the carbohydrate binding sites in rhodopsin, it should be accessible to the aqueous environment on one or the other side of the ROS disc. BIBLIOGRAPHIC REFERENCES: Papermaster, D.S., Converse, C.A., and Zorn, M. Biosynthetic and Immunochemical Characterization of a Large Protein in Frog and Cattle Rod Outer Segment Membranes. Exp. Eye Res. (1976) 23: 105-115. Fukuda, M.N., Papermaster, D.S., and Hargrave, P.A. Carbohydrate Moiety of Bovine Rhodopsin. Fed. Proc. (1977) 36: 895.